PARALLEL EVOLUTION OF LOCAL ADAPTATION AND REPRODUCTIVE ISOLATION IN THE FACE OF GENE FLOW

Parallel evolution of similar phenotypes provides strong evidence for the operation of natural selection. Where these phenotypes contribute to reproductive isolation, they further support a role for divergent, habitat‐associated selection in speciation. However, the observation of pairs of divergent ecotypes currently occupying contrasting habitats in distinct geographical regions is not sufficient to infer parallel origins. Here we show striking parallel phenotypic divergence between populations of the rocky‐shore gastropod, Littorina saxatilis, occupying contrasting habitats exposed to either wave action or crab predation. This divergence is associated with barriers to gene exchange but, nevertheless, genetic variation is more strongly structured by geography than by ecotype. Using approximate Bayesian analysis of sequence data and amplified fragment length polymorphism markers, we show that the ecotypes are likely to have arisen in the face of continuous gene flow and that the demographic separation of ecotypes has occurred in parallel at both regional and local scales. Parameter estimates suggest a long delay between colonization of a locality and ecotype formation, perhaps because the postglacial spread of crab populations was slower than the spread of snails. Adaptive differentiation may not be fully genetically independent despite being demographically parallel. These results provide new insight into a major model of ecologically driven speciation.     

STABILIZING SELECTION AND THE COMPARATIVE ANALYSIS OF ADAPTATION

Comparative studies tend to differ from optimality and functionality studies in how they treat adaptation. While the comparative approach focuses on the origin and change of traits, optimality studies assume that adaptations are maintained at an optimum by stabilizing selection. This paper presents a model of adaptive evolution on a macroevolutionary time scale that includes the maintenance of traits at adaptive optima by stabilizing selection as the dominant evolutionary force. Interspecific variation is treated as variation in the position of adaptive optima. The model illustrates how phylogenetic constraints not only lead to correlations between phylogenetically related species, but also to imperfect adaptations. From this model, a statistical comparative method is derived that can be used to estimate the effect of a selective factor on adaptive optima in a way that would be consistent with an optimality study of adaptation to this factor. The method is illustrated with an analysis of dental evolution in fossil horses. The use of comparative methods to study evolutionary trends is also discussed.     

RACES OF PERONOSPORA MANSHURICA IN THE UNITED STATES

I propose a set of 11 soybean varieties for the differentiation of races of Peronospora manshurica: Pridesoy, Norchief, Mukden, Richland, Roanoke, Illini, S 100, Palmetto, Dorman, Kabott, and Ogden. When I employed these, I found fifteen new races of Peronospora manshurica, the casual agent of downy mildew of soybeans, described them, and assigned numbers 9 through 23. Race 8 was encountered most frequently and occurred at 40% of the locations from which seed samples were obtained. Races 1, 2, 10, 12, 18, and 23 occurred at 5–8% of the locations sampled. Race 10 was common in the southern U. S. Of 247 soybean seed lots sampled, 73% contained some oospore-encrusted seeds. These ranged from 12–26% lighter than healthy seeds. The percentage of oospore-encrusted seeds occurring in seed lots ranged from 0–25%.     

THE DISCOLORATION OF ROOFS IN THE UNITED STATES AND CANADA BY ALGAE1

Roof shingles are often colonized and discolored by blue-green and green algae. The former are mostly subaerial species and the latter are soil algae most frequently recovered from the atmosphere.     

REHABILITATION AND RELEASE OF MARINE MAMMALS IN THE UNITED STATES: RISKS AND BENEFITS

Rehabilitation of stranded marine mammals elicits polarized attitudes: initially done alongside display collections, but release of rehabilitated animals has become more common. Justifications include animal welfare, management of beach use conflict, research, conservation, and public education. Rehabilitation cost and risks have been identified that vary in degree supported by data rather than perception. These include conflict with fisheries for resources, ignorance of recipient population ecology, poor understanding of long-term survival, support of the genetically not-so-fit, introduction of novel or antibiotic-resistant pathogens, harm to human health, and cost. Thus facilities must balance their welfare appeal against public education, habitat restoration, human impact reduction, and other conservation activities. Benefits to rehabilitating marine mammals are the opportunity to support the welfare of disabled animals and to publish good science and so advance our understanding of wild populations. In specific cases, the status of a population may make conservation the main reason for rehabilitation. These three reasons for rehabilitation lead to contrasting, and sometimes conflicting, management needs. We therefore outline a decision tree for rehabilitation managers using criteria for each management decision, based on welfare, logistics, conservation, research, and funding to define limits on the number of animals released to the wild.     

A SUMMARY OF THE TAXA IN THE VASCULAR FLORA OF THE UNITED STATES,CANADA AND GREENLAND

A tabular summary, by family, of the 56,431 computerized names of those native and naturalized plant taxa included in the “Synonymized checklist of the vascular flora of the United States, Canada and Greenland” (including Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands) indicates a flora of 21,588 species in 2,921 genera in 254 families. There are also 740 named hybrids and, under current concepts, 2,491 subspecies and 8,008 varieties in our flora. There are 20,429 pertinent or “manual level” synonyms, with the number of synonyms exceeding the number of accepted names in many families (especially those families of high agricultural, horticultural or other economic importance).